1. Field of the Invention
The present invention relates to an optical recording medium manufacturing master recording apparatus which condenses and irradiates a beam on a resist to thereby form a desired recording pattern.
2. Description of the Related Art
As optical recording media for recording audio, video and other various kinds of information, there is an optical recording medium of a ROM (Read Only Memory,) type, a write-once type, a rewritable type and the like such as an optical disc, an optical card, a magneto-optical disc, a phase change optical recording medium disc in which recording or reproduction thereof is performed by a light irradiation and the like, and for example, in a ROM type like a compact disc, minute convexes and concaves such as phase pits, pregrooves and the like for recording data information, a tracking servo signal and the like are formed or in the optical recording media such as the write-once type, the rewritable type and the like, the minute convexes and concaves such as the pregrooves and the like are formed.
When a substrate of the optical recording medium on which the minute convexes and concaves are formed is manufactured, it is manufactured by a stamper having a surface with convexes and concaves corresponding to the convexes and the concaves in compression molding, injection molding or the like. The stamper is duplicated by giving metal plating on a master for an optical recording medium and then peeling it off.
In the following one example of a process for manufacturing the master for the optical recording medium will be explained. In this example, an explanation will be made of a case where a predetermined pattern is formed by carrying out irradiation of a light particularly on a photoresist.
As is shown in FIG. 1, for example, a glass substrate 10 whose surface is adequately smoothly ground is mounted on a rotating base (not shown graphically), and a photoresist 11 which is soluble in alkalis is uniformly coated thereon as thick as, for example, about 0.1 xcexcm, as FIG. 2 shows, in a state that the substrate is revolved at a predetermined rotation speed.
The photoresist 11 is, as shown in FIG. 3, exposed to a predetermined pattern by a laser beam L. The exposure is carried out by feeding the laser beam L by an equal distance per one revolution in a radius direction of the glass substrate 10 while revolving the glass substrate 10 to generate a latent image of a groove on the resist 11 at a constant interval in a spiral state or a concentric circle state.
Next, as is shown in FIG. 4, the glass substrate 10 is developed in an alkaline developing solution and then, the exposed portion is removed. Being done in this manner, a master 20 for an optical recording medium, on which a predetermined pattern 11a with the minute convexes and concaves is formed is obtained on the glass substrate 10.
A schematic arrangement of an optical recording medium manufacturing master recording apparatus which carries out the pattern exposure by irradiating an exposure beam on a photoresist is shown in FIG. 5.
In an optical recording medium manufacturing master recording apparatus 100, there is provided a structure in which an objective lens 102 which condenses a laser beam spot and the like blinking in response to a recording signal and irradiates the same on the surface of, for example, a substrate 10 placed on a revolving base 101 is supported by using an elevator mechanism 105 consisting of a parallel plate spring and the like, and controlled in driving by a displacement driving mechanism 104 such as a voice coil motor and the like, so that the position of the objective lens 102 can be flexibly changed in a height direction of the substrate 10, that is, in a direction perpendicular to the surface of the substrate.
In the conventional optical recording medium manufacturing master recording apparatus 100, when the focus of the irradiating spot on the surface of the substrate 10 on the revolving base 101 deviates and a deviated amount of the spot is dected, this detection can be carried out by using detecting methods such as an off axis method, an astigmatism method and the like with the use of a laser beam having a different wavelength from that of the irradiated laser beam or by using a method which measures an electrostatic capacitance in a clearance between the substrate 10 and the objective lens 102.
In this case, since the revolving base 101 and the substrate 10 are controlled at high accuracy as to the degree of parallel and plane, a height adjustment of equal to or less than several xcexcm is made possible.
However, since the master 20 is repeatedly used, when a reproducing process such as regrinding and the like is carried out after it is once used, there are produced about several tens of xcexcm of changes in thickness when compared with an unused one.
Also, when the objective lens 102 in the conventional optical recording medium manufacturing master recording apparatus 100 is used to irradiate a recording beam on the substrate 10 to carry out an exposure, since it is necessary to form a minute condensed beam spot, the diameter of the condensed beam spot is made approximately equivalent to a wavelength of an electromagnetic wave or nearly a wavelength of the exposure beam.
In this case, it is necessary to make a numerical aperture NA of the objective lens 102 high, that is, the NA equal to nearly 0.9, and the depth of focus for maintaining the diameter of the condensed beam spot at a constant value is controlled to be equal to or less than about 0.1 xcexcm.
In this case, the interval between the objective lens 102 and the substrate 10 is made to be equal to or more than about 100 xcexcm.
By carrying out rough positioning of the height of the objective lens 102 by an elevator mechanism 105 which is capable of carrying out height adjustments, and thereafter, when the displacement driving mechanism 104 is driven in order to carry out, depending on necessities, a focus adjustment by the change amount in height of the substrate 10 and the revolving base 101, if a movable range by the displacement driving mechanism 104 is made equal to or less than 100 xcexcm, it was possible to prevent the objective lens 102 from coming in contact with the master 20.
However, due to the higher recording densification of recent optical recording media, there has occurred a necessity to form a more minute pattern. As a result, the clearance between an irradiating mechanism which carries out condensation and irradiation of a beam and a substrate which is subjected to an exposure of the beam has become narrower.
That is, since the distance between the substrate and the objective lens becomes narrower, the height adjustment of the objective lens becomes fine and as a result, there has occurred a danger that the objective lens and the substrate come in contact with each other, thereby incurring a fear that the substrate and the objective lens are damaged.
Then, an object of the present invention is, in view of the above-mentioned conventional situation, in a case where the formation of the recording pattern is carried out by condensing and irradiating the beam on the substrate by the irradiating mechanism such as the objective lens and the like, to effectively avoid the contact between the substrate and the objective lens.
According to an aspect of the present invention, there is provided an optical recording medium manufacturing master recording apparatus which has such an arrangement comprising a revolving base for placing a substrate coated with a resist thereon and revolving the substrate, an irradiating mechanism for converging and irradiating a recording beam on the resist, an elevator mechanism which makes it possible for the irradiating mechanism in an opposing portion to said substrate to move in a vertical direction relative to the revolving base as well as in a surface direction which is perpendicular to the vertical direction and a height position displacement mechanism which interposes between the irradiating mechanism and the elevator mechanism, in which the irradiating mechanism is connected to the elevator mechanism through the height position displacement mechanism and at the same time, the irradiating mechanism has such a structure in which at least the converging system and the displacement driving mechanism for adjusting a focus are supported by a gas static pressure pad housing, in the gas static pressure pad housing a gas feeding pad is disposed facing a bottom surface opposing the substrate, and gas is to be fed between the irradiating mechanism and the above-mentioned master through the gas feeding pad.
According to the optical recording medium manufacturing master recording apparatus, since gas is fed between the irradiating mechanism and the master, when the distance between the irradiating mechanism and the master becomes narrower, pressure there between is raised, thereby making it possible to push up the irradiating mechanism on the surface of the substrate. As a result, the distance between the irradiating mechanism and the master can be adjusted and maintained at a desired value.